Heating of fluids



March 30, 1937. M. w. BARNES HEATING OF FLUIDS Filed June '7, 1954 INVE TOR MAR N BARNES TORNEY I l I Y I l l l l l l I l Patented ar. 30, 1937 HEATING or FLUIDS lvlarion W. Barnes, Chlcago,lll., as slgnor to Unlvcrsal Oil Products Company, Chicago, 11]., a corporation of Delaware Application June "I, 1934, Serial No. 729,361

12 Claims.

This invention particularly refers to an improved method and means of heating fluids such as hydrocarbon oils to the high temperatures required for their conversion and more particularly conversion temperature attained by the oil in the first mentioned combustion zone.

One of the principal problems in the design of furnaces of the character above described, where- 2 in theoil is first heated to the desired conversion temperature and then maintained at or near the attained temperature for a predetermined time,

has been the large drop'in pressure due to friction through the fluid conduit, which is news-- 25 sarily of unusual length due to the time element required in the soaking section, 1. e. that section wherein the oil is maintained at a fairly constant temperature for a predetermined time. This necessitates exceptionally high pressures in the Q first heating stages in order to maintain the desired conversion pressure in the soaking section and obviously greatly increases pumping costs as well as necessitating the use of thicker wall tubes and fittings to maintain the proper safety factor 35 and obviate unusual fire and explosion hazard. An increase in the diameter of the fluid conduit for the purpose of reducing the pressure drop for a given volume of oil flowing therethrough, clue to friction, greatly reduces the effectiveness of 40 the heating surface measured over a given tube area, since the cross-sectional area, which determines the volume of the tube, increases out of proportion to the increased circumference, whichdetermines the heating surface. Therefore, the heating'surface per unit volume of oil undergoing treatment is decreased by increasing the tube diameter.

In the present invention in order to maintain the desired ratio of heating surface to tube volume or volume of oil undergoing treatment without an excessive pressure drop, due to friction through the fluid conduit, the stream of oil dur- .ng its passage through a major portion, at least, of the fluid conduit is divided into a plurality of substantially equal streams, parallel rows of tubes of theusual size being employed for the various streams.

In that portion of the fluid conduit subjected to heating by contact with combustion gases from 5 both combustion zones of the furnace, wherein the incoming oil is heated to below conversion temperature or to a relatively mild conversion temperature, the total volume of oil supplied to the furnace may be split into two or more streams of substantially equal volume each of which is passed simultaneously and in series through an equal number of tubes comprising similar portions of said fluid conduit, each of said similar portions being subjected to substantially the same 1 heating conditions.

That portion of the fluid conduit wherein the oil is brought to or near thedesired maximum conversion temperature may comprise, for example, a single horizontal row of horizontally disposed tubes located along the floor of one combustion zone of the furnace and a single horizontal row of horizontally disposed tubes located along the roof of the same combustion zone. In accordance with the present invention, the total volume of oil having passed through the previously mentioned portion of the fluid conduit, to which the incoming charging stock is supplied, may be split into two streams of substantially equal volume, one of which is passed in series through adjacent tubes comprising said row of tubes alongthe floor of the combustion zone while the other stream is passed in series through adjacent tubes comprising said row of tubes along the roof of the combustion zone. Since the row of tubes adjacent the floor of the combustion zone is normally exposed to more severe heating conditions than the row 'of tubes adjacent the roof of the combustion zone the stream of oil supplied to the roof bank is preferably passed through a 40 greater number of tubes in this bank than those employed for heating the other stream of oil in the floor bank, and/or, when desired, a somewhat greater volume of oil may be supplied to the floor tubes than to the roof tubes. Furthermore, in order to insure that both streams of oil from this portion of the fluid conduit enter the soaking section of the furnace at the same temperature I preferably commingle the two streams and pass 5 the commingled stream in series through several tubes located adjacent the roof of the furnace, prior to its introduction into the soaking section.

In the preferred embodiment of the present invention, that portion of thefluid conduit wherein 5 the highly heated hydrocarbon oil is maintained for a predetermined time at a temperature near the maximum conversion temperature previously attained preferably comprisesparallel shielded and exposed horizontal rows of horizontally disposed tubes located adjacent the roof of the other combustion zone of the furnace and parallel exposed and shielded horizontal rows of horizontally disposed tubes located adjacent the floor of said combustion zone.- In accordance with the invention, in order to minimize. friction and pressure drop through this portion of the fluid conduit and in order to uniformly heat the totalvolume of oil supplied therethrough, the highly heated oil entering this portion of the fluid conduit is preferably split into two streams of substantially equal volume each of which is passed through an equal number of exposed and shielded tubes. This may be accomplished, for example, by .employing' a criss-cross flow through the shielded and exposed rows of tubes, each of the two streams passing, for example, first through a tube in the exposed row and then through a tube in the shielded row of the roof bank, then through another tube in the exposed row and so on throughout the length of the two rows of tubes adjacent the roof and floor of the combustion zones; different streams of oil flowing through adjacent tubes in each row and the number of shielded tubes and exposed tubes in each row being equal. In this manner regardless of different heating conditions in the exposed and shielded rows and even though heating conditions may vary in different portions of the same row sub-' stantially equal heating is obtained in both streams and, due to equal heating and equal friction in each stream. a substantially equal quantity of ofl may be maintained in each stream.

In one embodiment, the invention comprises 40 dividing a stream of hydrocarbon oil to be subjected to conversion into a plurality of substantially equal streams, passing each stream simul-- taneously and in series through an equal number of tubes in similar sections of a fluid conduit, each section being subjected to substantially equal heating conditions by contact with commingled hot combustion gases from two separately fired combustion and heating zones of a furnace, whereby each stream of oil is subjected to substantially equal heating conditions, then passing the heated oil in two streams of substantially equal volume through a fluid conduit comprising rows of tubes located adjacent the roof and floor of one combustion zone of the furnace, one stream of oil passing in series through the tubes adjacent the floor and the other stream of oil passing in series through the tubes adjacent the roof, whereby each stream is subjected to substantially equal heating conditions by predominantly radiant heat from materials undergoing combustion in said combustion zone and hot refractory walls of the furnace and whereby the total oil is brought to near the maximum desired conversion temperature, then commingling the two streams of highly heated oil and passing the same through a plurality of tubes located adjacent the roof of ,the furnace whereby the temperature of the two streams is equalized, then dividing the stream of highly heated oil into two streams of substantially equal volume and passing the same. in series through tubes comprising shielded and exposed rows of tubes located adjacent the roof and floorof the other combustion zone in such a manner that each stream is passed through an equal number of shielded and exposed tubes, whereby each stream is subjected to substantially equal heating conditions by primarily radiant heat from mate-; rials undergoing combustion in said combustion zone and the hot refractory walls of the furnace; the heating in the last mentioned combustion zone" being of sufiicient intensity to maintain the oil at a substantially uniform temperature approaching the maximum to which it is subjected during its passage through the fluid conduits in this portion of the furnace.

The accompanying diagrammatic drawing is a sectional elevatio in cross-section of one specific form of furnace\ mbodying the various features of the present inv tion and in which the process of the invention a Kthe desired results may be accomplished.

Referring to the drawn}: the outer walls of the furnace are indicated at l and comprise the usual side walls, end-walls, roof and floor of any 'desired standard construction. The interior of the furnace comprises two combustion zones designated, respectively, as 2 and 3 and a convection heating zone 4, which latter is separated from the combustion zones 2 and 3 by the respective bridge walls 5 and 6.

Fuel is supplied by means of any suitable form of burners 23 through one or, preferably, a plurality of flring tunnels I to each of the combustion'zones 2 and 3. Any suitable fuel such as oil, gas or pulverized solid fuel being supplied, together with a portion of the air required for combustion, through the central portions or combustion compartments 8 of the tunnels while the desired auxiliary air is supplied to the combustion zone through tunnels 9 and II adjacent the central tunnel 8 and regulated'by means of suitable dampers H.

undergoing combustion from tunnel 8, assisting in controlling the combustion conditions and particularly the character of the flame in combustion zones 2 and 3 of the furnace.

The materials undergoing combustion in zones 2 and 3 of the furnace give up a major portion of their radiant energy to the fluid conduit located along the floor and roof of the combustion zone, as will be later more fully described, by means of which predominantly radiant heat is transmitted The air admitted through tun- Y nels 9 and Ill commingles with the fuel and airto the oil passing through the fluid conduit. The

combustion gases pass from combustion zones 2 and 3 over the bridge walls 5 and 6, respectively, and pass thence downward through the so-called convection heating zone 4 of the furnace where they give up heat largely by convection, although to some extent by radiation, to the fluid conduit in this portion of the furnace and to the oil passing therethrough. The spent combustion gases pass from convection zone I through flue l2 to a stack (not shown).

A bank I3 of horizontally disposed tubes l4 arranged in horizontally parallel rows is located in convection zone 4 of the furnace and, in the particular case here illustrated, is divided into eight similar vertical sections through each of which a separate stream of oil is passed, each stream being of substantially equal volume. Adjacent tubes in each vertical section of bank I3 are connected in series at their ends by means of suitable headers or return bends (not shown) preferably located outside the heating zone. The stream of oil to be subjected to heating and conversion is supplied to the furnace from any suitable source in a single stream indicated in the drawing by lines [5 and l 6. This stream is then split into two substantially equal streams, one designated'as l I and aerator the other as It, controlled by the respective valves l and it, each of which are again split, as indicated in the drawing, into two substantially equal streams and then four substantially equal streams 5 so that eight substantially equal streams of oil now through the eight similar sections of tube bank It. The eight streams of oil having passed through bank I! are recombined to form two substantially equal streams again designated as II 1 and It. The single lines I! and it throughout the drawing indicate substantially equal streams of oil. The dotted portions of these lines designate connections between adjacent tubes and between different portions of the fluid conduit on the far side of the furnace and the solid portions indicate the connections on the near side of the furnace. The arrows on these lines indicate the general direction of flow in each stream.

A single horizontal row ll of horizontally disposed tubes I4 is located along the floor of combustion zone 2. Preferably, as illustrated, this tube bank is depressed somewhat below the outlet from firing tunnel i so that it is out of the direct path of the materials undergoing combustion from this zone. The stream ID from tube bank I3 is passed in series through adjacent tubes of bank ll, flowing, in the case here illustrated, in a general direction counter-current to the direction of firing. A single horizontal row I! of horizontally-disposed tubes ll islocated along the roof of the furnace above combustion zone 2 and convection zone 4. The stream 16 from tube bank l3 passes in series through adjacent tubes in the major portion l8 of tube bank l8 in a general direction concurrent to the direction of firing in combustion zone 2 and then commingles in the remaining tubes of bank I8, comprising the section of this bank designated in the drawing as [8", with stream l5 from tube bank H, the commingled streams flowing in series through adjacent tubes of section l8" to subsequent portions of the fluid conduit which will be presently described.

The oil passing through banks l1 and it is heated, primarily by radiation from the combustion gases and hot refractory walls of the furnace, to or near the maximum conversion temperature to which it is desired to subject the oil and, preferably, relatively high rates of heating are employed in this portion of the fluid conduit so that the oil is brought quickly to the desired temperature.

Two parallel horizontal rows l9 and 20 of tubes ll comprise that portion of the soaking section of 0 the fluid conduit located adjacent the roof of combustion zone 3. The commingled streams l5 and it from section l8" of the fluid conduit are again split into two substantially equal streams designated as l5" and i6", stream l5" entering the end tube of bank 20 and stream l8" entering the adjacent tube of the same bank. The respective streams then pass in parallel through adjacent tubes'in shielded row l9, thence through the next two adjacent tubes in exposed row 20 and so on throughout this portion of the fluid conduit.

Parallel horizontal rows 2| and 22 of tubes ll comprise the remainder of the soaking section of the fluid conduit and are located adjacent the floor 0 of combustion zone 3. As in the case of floor bank ll, these tube: are preferably depressed somewhat below the outlet from the flring tunnel to remove them from the direct path of the materials undergoing combustion. The two streams of oil I5" 75 and it" from banks l9 and 20 flow through the tubes in the shielded and exposed rows 28 and 22, respectively, of the floor bank in a manner similar to that described, in connection with rows i9 and 20 of the roof bank. The two streams again commingle in the final shielded tube ll of the floor bank from which the single stream, designated as I!" and i6", of heated oil is discharged to any desired further stage of the cracking process.

It will be noted that the two substanti equal streams l5" and it" are subjected t substantially equal heating conditions in the soaking section of the fluid conduit comprising shielded rows l9 and 2| and exposed rows 20 and 22 in combustion zone 3. The two streams flow in parallel through adjacent tubes in both the shielded and exposed rows insuring that any unequal heating conditions in different zones along the heating coil will not produce different heating conditions in the two streams; furthermore, the number of shielded tubes in each stream is equal to the number of shielded tubes in the other stream and the number of exposed tubes in each stream is equal to the number of exposed tubes in the other stream, obviating any inequality in the heating of the two streams, due to different heating conditions in the shielded and exposed rows of tubes.

Preferably relatively mild heating conditions are employed in combustion zone 3 suillcient only to maintain the oil flowing through the fluid conduit in this zone at a substantially constant temperature near the maximum temperature attained in the preceding portion of the fluid conduit.

It will be understood that various modifications of the specific form of apparatus illustrated and I the specific flow above described may be employed I a without departing from the scope of the invention. For example, a fewer number of parallel streams may be employed, when desired, in bank l3, also, when desired, the general direction of flow of the oil through this zone may be concurrent to the flow of combustion gases instead of countercurrent. Furthermore, the direction of flow of oil through either or both of tube banks i1 and I8 may be reversed, when desired. Valves I5 and IS in streams l5 and I6, respectively, permit variations in the quantity of oil supplied through each of these streams, when desired, in order to insure a substantially equal temperature in each stream as they enter the soaking portion of the fluid conduit and it is within the scope of the present invention, when desired, to use section l8" of bank ill for heating either stream l5 or iii to the exclusion of the other stream. It is also specifically within the scope of the present invention, when desired, to omit the tubes in rows 18, I9 and 20 which are located above and opposite to the tubes in bank I3. When these tubes are omitted a higher proportion of radiant heat will be imparted to the tubes in the upper rows of bank l3 and consequently a somewhat higher rate of heating will be obtained in this portion of the fluid conduit.

I claim as my invention:

1. A furnace for heating fluids which comprises, in combination, two combustion zones, means for independently controlling the heating conditions in each combustion zone, a convection zone, means for supplying combustion gases from both combustion zones to the convection zone, a plurality of elongated tubular elements located within the convection zone,

from the combustion gases, a plurality ot/elongated tubular elements located adjacent the root of each combustion zone and'heated predominantly by radiant heat, a plurality of elongated tubular elements located adjacent the floor 01 each combustion zone and heated predominantly by radi= antheat means' for passing fluid to be heated in a plurality or separate streams oi! substantially equal volume through the tubular elements in the convection zone, means for'passing separate portions of the fluid undergoing treatment in two separate substantially equal streams through the',

conditions in each combustion zone, a convection zone, means for supplying combustion gases from both combustion zones to the convection zone, a fluid conduit comprising a plurality of elongated tubular elements located within the convection zone, means for heating said fluid 0 conduit by, heat from the combustion gases, a

fluid conduit comprising a single row of elongated tubular elements located adjacent the floor of one combustion zone, a fluid conduit comprising a singlerow of elongated tubular elements located adjacent the roof of the same combustion zone, a shielded row and an exposed row of elongated tubular elements located adjacent the roof and adjacent the floor of the other combustion: zone, means for passing the fluidto be heated in a plurality of substantially; equal streamsthrough similar portions of the fluid conduit located within the convection zone, each of said sections being subjected to substantially equal heating conditions, means for then passing the fluid in two substantially equal streams through the fluid conduits located adjacent the roof and floor of the first mentioned combustion zone, one stream flowing through the row of tubes adjacent the roof and the other stream flowing through the row of tubes adjacent the floor, each stream being heated to substantially the same temperature and means for then passing thefluid in two substantially equal streams through said shielded and exposed rows located adjacent the roof and floor of the other combustion zone, each stream flowing through an equal number of exposed tubes and each stream flowing through an equal number of shielded tubes whereby the two streams are subjected to substantially equal heating conditions in this zone.

3. A furnace for heating fluids which comprises, in combination, two combustion zones, means for independently controlling the heating conditions in each combustion zone, a convection zone, means for supplying combustion gases from both combustion zones to the convection zone, a fluid conduit comprising a plurality of elongated tubular elements located within the convection zone, means for heating said fluid conduit by heat from the combustion gases, a fluid conduit comprising a single row of elongated tubular elements located adjacent the floor of one combustion zone, a fluid conduit comprising a single row at elongated tubular 9,075,001 meansv for heating'said elements by heat;

elements located adjacent the roof of the same combustion zone, a shielded row and an exposed row .0! elongated-tubular elements located adjacent the roof and adjacent the floor oi' the other combustion zone, means for passing the fluid to be heated in a plurality of substantially equal streams through similar portions of the .fluid conduit located within the convection zone,

each of: said sections being subjected to substantially' equal heating conditions, means for 'then passing the fluid in two substantially equal streams through the fluid conduits located adjacent the root and floor oi the first mentioned combustion zone, one stream flowing through the row of tubes; adjacent the root and the other stream flowing through the row of tubes'adjacent the floor, means for commingling the stream or fluid having passed through the row of tubes adjacent the floor with the stream of fluid passing throughgthe row of tubes adjacent the roof in at least one tube of said row adjacent the roof and means for then passing the fluid in two substantially equal streams throughsaid shielded and exposed rows located adjacent the root and floor of the other combustion zone, each stream flowing through an equal number 01- exposed tubes and each stream flowing through an equal number of shielded tubes, whereby the two streams are subjected to substantially equal heating conditions in this zone.

4. A furnace vfor heating fluids which comprises, in combination, two combustion zones, means for independently controlling the heating conditions in each combustion zone, a convection zone, means for; supplying combustion gases from both combustion zones to the convection zone, a fluid conduit comprising a plurality ofelongated tubular elements located within theconvectionfzone, means for heating said fluid conduit byhe'at from the combustion gases, a fluid conduit comprising a single row of elongated tubular. ,elementslocated adjacent the floor of one combustion zone, a fluid conduit comprising a single row of elongated tubular elements located adjacent the roof oi! the same combustion zone, a shielded row and an exposed 'row of elongated tubular elements located adjacent the roof and adjacent the floor of the othercombustion zone, means for passingthe fluid to be heated in a plurality of substantially equal streams through similar portions of the fluid conduit located within the convection zone, each of said sections being subjected to substantially equal heating conditions, means for then passing the fluid in two substantially equal streams through the fluid conduits located adjacent the roof and floor of the first mentioned combustion zone, one stream flowing through the row of tubes adjacent the roof and the other stream flowing through the row of tubes adjacent the floor, means for commingling the stream of fluid having passed through the row of tubes adjacent the floor with the stream of oil passing through the row of tubes adjacent the roof in at least one tube of said row adjacent the roof and means for then passing the fluid in two substantially equal streams through said shielded and exposed rows located adjacent the roof and floor of the other combustion zone, each stream flowing through an equal number of exposed tubes, each stream flowing through an equal number of shielded tubes and the two streams flowing in parallel through adjacent tubes in the shielded row and adjacent tubes in the exposed row;

5. In a process for the pyrolytic conversion of relatively low boiling hydrocarbon oils, the method of heating which comprises dividing a stream of said oil into a plurality of substantially equal streams, passing each of said substantially equal streams simultaneously through an equal number of tubes in similar sections of a fluid conduit, each section being subjected to substantially equal heating conditions by contact with 10 commingled hot combustion gases from two separately fire-d combustion and heating zones of a furnace, whereby the total oil is substantially uniformly heated to a relatively mild conversion temperature, then passing the heated oil in sepa- 15 rate streams of substantially equal volume through separate fluid conduits comprising rows of tubes located adjacent the floor and roof of one combustion zone of the furnace, each stream being subjected to substantially equal heating 20 conditions whereby the total oil is substantially uniformly heated to a relatively high conversion temperature, then commingling the separate streams of highly heated oil and passing the same through at least one tube in the fluid con- 25 duit located adjacent the roof whereby the temperature of the separate streams is equalized, then dividing the stream of highly heated oil into separate streams of substantially equal volume and passing each simultaneously through 3 tubes located adjacent the roof and floor of. the

other combustion zone, each stream being subjected to substantially equal heating conditions whereby the total oil is maintained for a predetermined time at asubstantially uniform con- 35 version temperature near the maximum to which it is subjected.

v6. A process of the character defined in claim 5 wherein the relative volume of each of said separate streams of oil supplied to the fluid conduits 40 in the first mentioned combustion zone is regulated to compensate for any inequality in the heating conditions to which the separate streams are subjected in this zone of the furnace.

'7. A furnace for heating fluids comprising a 45 pair of combustion zones and a'convection zone, means for passing combustion gases from both said combustion zones through the convection zone, a plurality of heating tubes in the convection zone, a row of serially connected floor 50 tubes. and a row of serially connected roof tubes in one of said combustion zones, additional heating tubes in the other of said combustion zones, means for passing the fluid to be heated in a plurality of streams through the tubes in the 55 '7 ion zone, means for passing a portion of the thus heated fluid through said floor tubes and another portion thereof through said roof tubes, and means for then passing the fluid through said additional tubes.

60 8. A furnace for heating fluids comprising a pair of combustion zones and a convection zone, means'for passing combustion gases from both said combustion zones through the convection zone, a plurality of heating tubes in the convec- 5 tion zone, a row of serially connected floor tubes and a row of serially connected roof tubes in one of said combustion zones, additional heating tubes in the other of' said combustion zones, means for passing the fluid to be heated in a plurality of streams through the tubes in the convection zone, means for passing a portion of the thus heated fluid through said floor tubes and another portion thereof through said roof tubes, and

means for then passing the fluid in separate streams through said additional tubes.

9. In a furnace having a combustion zone and a convection zone adapted to receive combustion gases from the combustion zone, the combination of a plurality of banks of heating tubes so arranged in the convection zone as to be substantially uniformly heated by said gases, a row of serially connected floor tubes and a row of serially connected roof tubes in the combustion zone, means for passing fluid to be heated in a plurality of parallel streams through the banks of tubes in the convection zone, and means for passing some of said streams in admixture through said floor tubes and for passing others thereof in admixture through said roof tubes.

10. In a furnace having a pair of independently fired combustion zones, the combination of a row of serially connected floor tubes and a row of serially connected roof tubes in one of said zones, additional tubes in the other of said zones, means for passing a stream of fluid to be heated through said row of floor tubes and another stream thereof through the row of roof tubes and for then combining the separate streams, and means for passing the thus heated fluid through tubes in said other zone.

11. In a furnace having a pair of independently fired combustion zones, the combination of a row of serially connected floor tubes and a row of serially connected roof tubes in one of said zones, two s eries of tubes in the other of said zones, means for passing a stream of fluid to be heated through said row of floor tubes and another stream thereof through the row of roof tubes and for then combining the separate streams, and means for passing a separate portion of the resultant mixture through each series of tubes in said other zone. h

12. In the subjection of hydrocarbon oils to conversion temperatures in a furnace having a pair of independently fired combustion and radiant heat zones, the method which comprises passing a stream of oil adjacent the floor and another stream adjacent the roof of one of said zones, then combining the streams and dividing the resultant mixture into separate portions, and subjecting these portions to substantially equal heating conditions in the other of said zones.

13. In the subjection of hydrocarbon oils to conversion temperatures in a furnace having a pair of independently fired combustion and radiant heat zones and a convection zone receiving combustion gases from both said'combustion' zones, the method which comprises uniformly heating separate streams ofthe oil in the convection zone, passing some of said streams in admixture adjacent the floor of one of said combustion zones, passing others of said streams in admixture adjacent the roof of the same combustion zone, and then subjecting all portions of the oil to substantially uniform heating conditions in the other of said combustion zones.

MARION W. BARNES. 

